<template>
  <div class="pagination">
    <button :disabled='pageNo'>上一页</button>
    <button 
        v-if="startNumAndEndNum.start > 1 "
        @click="$emit('getPageNo',1)"
        :class="{active : pageNo === 1}"
        >1</button>

    <button v-if="startNumAndEndNum.start > 2">···</button>
    <!-- 中间部分 -->
    <button
      v-for="(page, index) in startNumAndEndNum.end"
      :key="index"
      v-if ="page >= startNumAndEndNum.start"
      @click="$emit('getPageNo', page)"
      :class="{ active: pageNo == page }"
    >
      {{ page }}
    </button>
    
    <button v-if="startNumAndEndNum.end < totalPage - 1">···</button>
    <button
        v-if="startNumAndEndNum.end < totalPage"
        @click="$emit('getPageNo', totalPage)"
        :class="{active:pageNo==totalPage}"
    >
        {{totalPage}}
    </button>
    <button
        :disabled="pageNo == totalPage"
      @click="$emit('getPageNo', pageNo + 1)"
    >下一页</button>
    
    <button style="margin-left: 30px">共 {{total}} 条</button>
  </div>

</template>

<script>
    export default {
        name:'Paging',
        // pageNo:多少页  pageSize：一页展示多少条 
        //total：总条数   continues：页码起始结束数
        props: ['pageNo','pageSize','total','continues'],
        computed: {
            //总共多少页
            totalPage() {
                //向上取证
                return Math.ceil(this.total / this.pageSize);
            },
            //计算出连续的页码的起始数字与结束数字[连续页码的数字:至少是5]
            startNumAndEndNum(){
                const { continues, pageNo, totalPage } = this;
                //开始数字
                let start = 0
                let end = 0
                //不正常现象【总页数没有连续页码多】
                if(continues > totalPage){
                    start=1
                    end=totalPage
                }else{
                    //进入代表页数大于5

                    //起始
                    start = pageNo - parseInt(continues / 2)
                    //结束
                    end = pageNo + parseInt(continues / 2)
                    //纠正 起始数 为 负数或者是0
                    if(start < 1 ){
                        start = 1
                        end = continues
                    }
                    //纠正 结束数 大于总页数
                    if(end > totalPage){
                        end = totalPage
                        start = totalPage - continues + 1
                    }
                }
                return {start , end}
            },
        }
    }
</script>

<style scope lang="less">
  .pagination {
  text-align: center;
  button {
    margin: 0 5px;
    background-color: #f4f4f5;
    color: #606266;
    outline: none;
    border-radius: 2px;
    padding: 0 4px;
    vertical-align: top;
    display: inline-block;
    font-size: 13px;
    min-width: 35.5px;
    height: 28px;
    line-height: 28px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    border: 0;

    &[disabled] {
      color: #c0c4cc;
      cursor: not-allowed;
    }

    &.active {
      cursor: not-allowed;
      background-color: #409eff;
      color: #fff;
    }
  }
}
.active{
  background: skyblue;
}

</style>